Hachures

Hachures /ˈhæʃʊərz/ are an older mode of representing relief. They show orientation of slope, and by their thickness and overall density they provide a general sense of steepness. Being non-numeric, they are less useful to a scientific survey than contours, but can successfully communicate quite specific shapes of terrain. They are a form of shading, although different from the one used in shaded maps.

Hachure representation of relief was standardized by the Austrian topographer Johann Georg Lehmann in 1799. Hachures may be combined with other ways of representing relief, like shades, the result being a shaded hachure map; an example of such a map is the Dufour Map of Switzerland.Emil von Sydow designed maps with coloured hachures: green for lowlands and brown for highlands.

Hachures are strokes (short line segments or curves) drawn in the direction of the steepest slope (the aspect direction). Steeper slopes are represented by thicker, shorter strokes, while gentler slopes are represented by thinner, longer and farther apart strokes. A very gentle slope or a flat area, like the top of a hill, are usually left blank.

The hachures are traditionally monocolour, usually black, gray or brown. Using two complementary colours for the hachures on a neutral background colour (e.g. black and white lines on gray map colour) would give a shading effect as if the relief were illuminated.

In representing relief with hachures on a map, six rules are to be followed, according to G.R.P. Lawrence (1979):

The Swiss cartographer Eduard Imhof set 5 similar rules:

If the illumination is vertical, rule 5 is kept; in the case of oblique illumination, it is dropped. The rules above are to be obeyed for large-scale maps. If the map being drawn is a small-scale map (less than 1:500 000 according to Imhof), rules may be relaxed in order to obtain a more suggestive representation.

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